Re: Landing Page Relevance

Quality score, including all the factors that go into it, only update once there's enough data. So if you've a had a keyword running for a long time with a below average landing page experience, it will take time (and new clicks and impressions) for the average landing page experience to improve within the system.

Landing page experience also goes beyond having relevant text on the landing page, including page load time and mobile site performance.

Re: Landing Page Relevance

In addition to the great explanation from @CassieH, you should also take note that a higher bounce may definitely indicate bad user experience. The point is that if you optimize your landing page for your users and give them a great experience and at the same time make it relevant to your ads and keywords, the results are sure to be improve.

But it does take time to see updates in score. Meanwhile, I will advise you to focus on improving CTR as well. It will give you better QS.